Method and device for the extraction of substances from liquids or solids dispersions

ABSTRACT

In a method for extracting ingredients, particularly foreign substances, from liquids or solids dispersions by using compressed extraction agents such as, for instance, supercritical or liquid carbon dioxide, the liquid or dispersion is applied as a thin film in a pressure-tight reactor and the surface of the thin film is treated with the extraction agent, particularly carbon dioxide, wherein the surface of the thin film is constantly renewed over at least a portion of the layer thickness of the thin film by mechanically acting on said liquid or dispersion.

This Application is a national phase application of 371 ApplicationPCT/AT03/00246, filed Aug. 26, 2003, which claims the benefit ofAustrian patent application 1274/2002, filed Aug. 26, 2002.

FIELD OF THE INVENTION

The invention relates to a method for extracting components,particularly foreign substances or impurities, from liquids or solidsdispersions by using compressed extraction agents such as, for instance,supercritical or liquid carbon dioxide, as well as a device for carryingout said method.

BACKGROUND OF THE INVENTION

The extraction with supercritical gases has already been used on anindustrial scale for more than 20 years. Main applications include thediscontinuous processing of solids in the food industry. Continuousmethods for separating liquids by the aid of supercritical gases havealready been proposed too, wherein the field of application usinghigh-pressure columns is limited to liquids exhibiting low viscosities,no solids portions and no tendency to foaming or solids precipitationunder the applied conditions. Stirrers may be employed when usingviscous liquids, wherein blending as intensive as possible, of thesolvents and the liquid to be extracted is essential and liquid-liquidextractions, as a rule, require a number of auxiliary agents in order toappropriately reduce the viscosities of the liquids to be extracted. Theseparation of oils from lecithin is an example of a particularlydemanding extraction. In order to avoid the difficulties involved incolumns and to ensure, even with higher-viscosity liquids, that theextraction fluid will be intensively mixed in an appropriate manner withthe liquid to be extracted, spray-extraction methods have been proposed,in which the material to be extracted is contacted with thesupercritical fluid as extraction agent or solvent by being sprayed inthe form of extremely fine droplets. Yet, in order to ensure appropriatesprayability, elevated temperatures are usually required to lower theviscosity, a method of this type, thus, having its limits when employedwith temperature-sensitive substances. This applies also to molecularvapor distillation, which serves to separate useful materials fromhighly viscous media. During spraying, the droplets tend to rapidlyagglomerate anew, particularly if the liquids concerned are relativelyviscous, and hence a sufficiently intensive contact of the solvent willonly occur with the surfaces of such droplets. As a result, aconcentration gradient will rapidly form in the interior of thedroplets, whereby also the viscosity may accordingly vary due to theresulting different chemical composition throughout the radius, so thatan effective extraction will no longer be feasible from thecomparatively hard cores of such droplets.

SUMMARY OF THE INVENTION

The invention aims to expand the field of application of fluidextractions to media that have so far been only difficult to extract,and, in particular, render feasible the processing of structurallyviscous media, and to provide the option to process raw materials havingrelatively high solids portions. Especially the extraction of dispersesystems having high solids portions is hardly feasible by sprayingmethods without entailing the risk of the nozzles being obstructed. Evenslightly foaming products are to be processable by the method accordingto the invention, and is should be feasible during said method todestroy possibly formed foam.

To solve this object, the method according to the invention of theinitially defined kind consists essentially in that the liquid ordispersion is applied as a thin film in a pressure-tight reactor and thesurface of the thin film is treated with the extraction agent,particularly carbon dioxide, whereby the surface of the thin film isconstantly renewed over at least a portion of the layer thickness of thethin film by mechanically acting on said liquid or dispersion. Due tothe fact that the liquid or dispersion is applied as a thin film in apressure-tight reactor, the surface required for the attack by theextraction agent and the optimum mass transfer into the compressedextraction agent will be provided, whereby in this case, as in theextraction of sprayed droplets, the risk of a concentration gradientforming over the size of the layer thickness cannot, of course, beexcluded a priori. However, due to the fact that the surface of the thinfilm is constantly renewed by the mechanical treatment of said liquid ordispersion simultaneously with the treatment of the thin film with theextraction agent, it is feasible to exert shearing forces and millingforces on the film, which provoke accordingly high turbulences in theinterior of the film, thus constantly conveying to the surfacerespectively new partial regions of the layer thickness. The thin layerof the film is, thus, thoroughly worked through mechanically, wherein itis, at the same time, feasible by such mechanical devices to adjust therespectively desired layer thickness of the film. It is, thus,altogether feasible to constantly even out the respective distributionof the extractable substances within the film by mechanical treatmentand to continuously ensure optimum blending within the film, withpossibly forming lumps and aggregates being destroyed by mechanicaltreatment. In a particularly advantageous manner, the renewal of thesurface of the thin film is effected by the aid of wipers, rollers ordoctor blades while simultaneously adjusting the layer thickness so asto immediately provide the desired millability and hence the turbulencesdesired to take place within the film.

BRIEF DESCRIPTION OF THE DRAWINGS

The device according to the invention, for carrying out said methodincludes a pressure-tight reactor having at least one charging openingfor the liquid or dispersion to be treated and the compressed extractionagent as well as appropriate discharge openings, and is essentiallycharacterized in that the charging opening for the liquid or dispersionto be treated opens on the inner shell of the reactor, and that a rotoris arranged in the interior of the reactor, the radial arms of saidrotor cooperating with the liquid or dispersion film on the inner shellof the reactor. By using a reactor with a rotor arranged in its interiorit has become possible to provide the mechanical action also by theadditional action of centrifugal forces, whereby an accordingly rapidrotation may be ensured to apply the desired centrifugal forces. By thesimultaneous action of such centrifugal forces in the interior of thereactor, even foaming products can be processed in a particularlyadvantageous manner, and optionally formed foam can be effectivelydestroyed. At the same time, the rotor provides the tools for themechanical treatment of the thin film, which in the simplest case may becomprised of wipers, rollers, doctor blades or the like. In thisrespect, the configuration is advantageously devised such that theradial arms carry rods, scrapers, wipers or rollers extending in thedirection of the axis of rotation. Such rods, scrapers, wipers orrollers may naturally also be slightly inclined relative to the axis ofrotation, and this, in particular, if the reactor comprises asubstantially funnel-shaped, conical inner shell. Said rods, scrapers,wipers and/or rollers will preferably extend in a substantially axialdirection, if a substantially cylindrical reactor is used.

In order to provide a simple rotor drive, the configuration mayadvantageously be devised such that the rotor shaft is connected with adrive via a magnetic coupling.

In order to be able to readily apply the medium to be subjected toextraction, in a reactor of this type, close to the inner surface of thereactor wall, the configuration in an advantageous manner is devisedsuch that the charging opening is designed as a radial and axial boreprovided in a lid capable of being sealingly connected with the tubularreactor, wherein a sealing connection is ensured in a simple manner inthat the reactor is designed as a tube including flanges connected tothe tube ends, and that the lids capable of being sealingly connected ina pressure-tight manner are attachable to said flanges.

DETAILED DESCRIPTION OF THE INVENTION

In the following, the invention will be explained in more detail by wayof an exemplary embodiment of the device according to the invention forcarrying out the method of the invention, which is schematicallyillustrated in the drawing. In the drawing, a pressure-tight reactor,which is designed in a cylindrical or tubular manner, is denoted by 1.The reactor 1 can be closed in a pressure-tight manner by the aid of alid portion 2 and a bottom portion 3, the connection being realized viaflanges 4 and 5. In the lid portion 2, a stirrer 6 comprising a magneticcoupling for rotationally driving a stirrer shaft 7 is arranged. Thestirrer shaft 7, in turn, is connected with the rotor 8, which ismounted in the interior of the reactor 1 so as to be rotatable about anaxis of rotation 9. The respective guiding or centering of the rotor isrealized via a mandrel 10 firmly connected with the bottom portion 3.The rotor 8 carries several guide rods 11 arranged in a circularlydistributed manner, which serve to guide the rotationally mountedrollers 12 in a manner so as to enable the rollers 12 to roll down alongthe inner circumference 13 of the reactor 1 at a rotation of the rotor 8about the axis of rotation 9.

A charging opening 14 for the liquid or dispersion to be treated isprovided in the lid 2. The charging opening opens into the cylindricalreactor space in the region of the inner circumference 13 of the reactor1. By pressing in, via the charging opening 14, the liquid or dispersionto be treated, said liquid or dispersion is conveyed in the interior ofthe reactor 1 in the direction towards the discharge opening 15 whilebeing pressed downwards in the annular gap defined between the innercircumference 13 of the reactor 1 and the outer periphery of the rotor.In this region, the liquid or dispersion to be treated is mechanicallyacted on by the rotating roller 12 so as to cause an extremely thinliquid film to form between the rotating rollers 12 and the innercircumference 13 of the reactor 1. The thickness of the liquid film isdetermined by the preset distance of the rollers 12 relative to theinner shell 13 of the reactor 1. The rollers 12 may have helicalprofiles, yet may also be conically, concavely or convexly designed,said profiles, at the same time, promoting the downward movement of theliquid film in the direction towards the discharge opening 15 duringrolling down along the liquid film.

An extraction agent preferably comprised of liquid or supercriticalcarbon dioxide is introduced into the reactor in counterflow to theliquid or dispersion to be treated, the pertinent charging opening beingformed in the bottom portion 3 and denoted by 16. The extraction agentrises in the interior of the reactor 1 and gets into intensive contactwith the liquid film, with the liquid film surface exposed to theextraction agent being constantly renewed by the milling or kneadingprocedure induced by the rotating rollers 12. The extraction agentloaded with the extracted ingredient may subsequently be drawn off viathe discharge opening 17 provided in the lid 2.

A closeable opening 18 is additionally provided to allow for the takingof samples or the checking of various operating parameters duringoperation. Another such opening may also be provided in the bottomportion 3.

Furthermore, the pressure-tight reactor 1 is surrounded by heatingand/or cooling jackets 19 and 20, through which a heating and/or coolingliquid, respectively, and, in particular, water may pass in coflow with,or counterflow to, the liquid or dispersion to be treated.

1. A method for extracting impurities from liquids or solids dispersionsby using one of supercritical and liquid carbon dioxide as an extractionagent, the method comprising the steps of: applying the liquid ordispersion as a thin film in a pressure-tight reactor; and treating thesurface of the thin film with the one of the supercritical or liquidcarbon dioxide, in a counterflow direction, whereby the surface of thethin film is constantly renewed over at least a portion of a layerthickness of the thin film by mechanically acting on said liquid ordispersion by the aid of one of wipers, rollers or doctor blades, whilesimultaneously adjusting the thickness of the thin film, discharging theliquid or dispersion separately from one of the supercritical and liquidcarbon dioxide, and simultaneously adjusting the thickness of the thinfilm and promoting axial movement of the thin film toward a dischargeorifice by means of rollers having one of a helical, a conical, a convexand a concave profile.
 2. A device for extracting impurities fromliquids or solids dispersions by using one of supercritical or liquidcarbon dioxide as an extraction agent, including a pressure-tightreactor (1) having at least one charging opening (14) for the liquid ordispersion to be treated and the one of the supercritical and liquidcarbon dioxide (16) as well as separate discharge openings (15, 17),wherein the charging opening (14) for the liquid or dispersion to betreated opens on the inner shell (13) of the reactor (1), and that arotor (8) as radial arms which are arranged in the interior of thereactor (1) and carry at least one of rods (11), scrapers, wipers orrollers (12) extending in the direction of the axis of rotation (9), theradial arms of said rotor cooperating with the liquid or dispersion filmon the inner shell (13) of the reactor (1), and the charging opening forthe liquid or dispersion to be treated and the charging opening for theone of the supercritical and liquid carbon dioxide are arranged onopposite sides of the reactor, and a plurality of radial armsrotationally support a plurality of rollers (12) such that the rollers(12) are axially aligned adjacent the inner shell (13) of the reactor(1), the rollers (12) are spaced from the inner shell (13) of thereactor (1) by a preset distance, which defines a thickness of theliquid or dispersion film, and the rollers (12) having one of a helical,a conical, a concave and a convex profile to promote movement of theliquid or dispersion film to a discharge opening.
 3. The deviceaccording to claim 2, wherein the reactor (1) comprises a substantiallycylindrical or funnel-shaped conical inner shell (13).
 4. The deviceaccording to claim 2, wherein a rotor shaft (7) is connected with adrive (6) via a magnetic coupling.
 5. The device according to claim 2,wherein the charging opening (14) is a radial and axial bore provided ina lid (2) capable of being sealingly connected with the tubular reactor(1).
 6. The device according to claim 2, wherein the reactor (1) is atube which has flanges (4, 5) connected to the tube ends, and the lids(2, 3) capable of being sealingly connected in a pressure-tight mannerare attachable to the flanges (4, 5).